Upon tissue damage or infection, monocytes leave the bloodstream and are rapidly recruited to the tissue, where they differentiate into tissue macrophages. Part of the innate immunity, macrophages are specialized cells that recognize, engulf and destroy target cells or pathogens. They are remarkably plastic and can change their functional phenotype depending on the various microbes or invaders they encounter. Along with their ability to clear pathogens, macrophages can also instruct other immune cells to take part in the immune response by acting as an antigen-presenting cell (APC).

The isolation of mature macrophages from tissue can be difficult, therefore the use of monocyte-derived macrophages (MDM) for functional studies is a very attractive alternative. Non-monocytes are depleted from the mononuclear cell population using immunomagnetic particles leaving purified, untouched CD14+ monocytes. The untouched monocytes are cultured for 4-5 days with 10% FBS in the presence of M-CSF and IL-4. After culture, cells are checked for the expression of CD11b, CD18, CD68, and HLA-DR by flow cytometry.